Helicobacter hepaticus is identified as a gram-negative, microaerophilic, urease-positive, spiral bacterium. Helicobacter hepaticus has been found to cause a chronic active hepatitis in some strains of mice but only enteric infection without clinical or histological disease in other mouse strains. Of the other Helicobacter spp. of mice, H. rappini has not been associated with lesions in mice, H. muridarum has been observed in gastric glands of mice with chronic gastritis, and H. bilis was isolated from older mice and based on 16s rRNA gene sequence analysis was named as a new organism. Helicobacter hepaticus colonizes the bile, liver and intestine of the mice. The presence of this organism in the liver of mice and associated liver lesion has raised questions regarding the use of these mice in biomedical research. Animals harboring this organism may not be acceptable for research involving the liver and gastrointestinal tract. Diagnosis and eventual elimination of this organism from research animals has high priority. We have been able to isolate, culture and quantitate this organism from A/Jcr, DBA/2Ncr, and C57B/6 strain of mice and a rat strain. We are collaborating with the other laboratories to develop PCR and specific ELISA test to diagnose Helicobacter Spp. infection and to determine the best procedure for a routine rodent surveillance program.